User Equipments (UEs) are often used to measurement various parameters in a radio communications network including some sort of measure of signal quality of received symbols. There are many different types of signal quality measurements such as received signal strength indicator (RSSI), Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and others. In LTE, Reference Signal Received Quality (RSRQ) is defined in 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements,” TS 36.214, incorporated herein by reference, as a ratio N×RSRP/(E-UTRA carrier RSSI), where RSSI is measured (1) only in orthogonal frequency division multiplexed (OFDM) symbols containing reference symbols for antenna port 0 in the measurement bandwidth or (2) over all OFDM symbols in indicated subframes if higher layer signaling indicates certain subframes for performing RSRQ measurements. Ultimately, the RSRQ reported by the UE to the network is an average for the OFDM symbols include in a received OFDM subframe. This can be problematic in some scenarios.
One example scenario is Heterogeneous Networks (HetNets) which combine macro and pico base stations or other small cells within a wireless communication system. In a HetNet scenario with Remote Radio Unit (RRU), the pico base station transmission(s) are often synchronized with the macro base station transmission. Expanding the coverage range for a pico cell may be used to increase the amount of UE traffic handled by the pico cell and also to improve the quality of the uplink radio link and UE bit rate. Although locating several pico base stations within the cell coverage of a macro base station will typically increase the network capacity, interference between the macro and pico base stations must be managed. For example, a drawback with expanding the coverage range for a pico cell can be decreased quality and increased interference on the downlink.
Because such downlink interference can be severe, it may be desirable to protect control signaling on control channels like the Physical Data Control Channel (PDCCH). In LTE, the size of the PDCCH can be dynamically set per subframe which means that different coordination schemes can be used such as an Almost Blank Subframe (ABS) scheme or a fractional PDCCH load scheme to reduce transmissions on the PDCCH channel, thereby reducing downlink interference. The interference may also differ on different channels in the pico cell, e.g., the PDCCH may experience less interference than the Physical Data Shared Channel (PDSCH). Such coordination schemes typically result in undesirable interference patterns that undermine the performance of reliable measurements.
The RSRQ is based on RSSI measured on symbols across multiple different channels resulting in an average signal quality for multiple channels, which in this example includes the PDCCH, the Physical Control Format Indicator Channel (PCFICH), and the physical downlink shared channel (PDSCH). But this average signal quality may not be a satisfactory measure of the received signal quality for an individual one of those channels included in the average. For example, the detected average RSRQ on measured on the downlink subframe by the UE may not be an accurate measurement of the RSRQ on the PDCCH included in that downlink subframe. The quality per individual channel depends on the interference difference which cannot be identified and removed when the interference over the symbols on which the signal quality is measured is unknown.